Need help downgrading from 10.5 to 10.4

Hello. I'm fairly new to mac and I need to downgrade from 10.5 to 10.4. I put in the black disc labeled "Mac OS X Tiger 10.4.6 Install DVD" but it tells me "Mac OS X 10.4 cannot be installed on this machine." Anyone know other ways to try?

The version of OS X and install disk\recovery disk is specific to your machine. It's possible to downgrade from Leopard to Tiger if you purchase a retail version of Tiger, boot with it, erase the current operating system along with all its applications and data, and then install Tiger.

But, why would you want to do that? If the machine is running Leopard, leave it alone. OS X is not like Windows where it might be desirable for example to downgrade from Vista to XP.